1. Field of the Invention
The present invention relates to a memory element and a semiconductor device having the memory element.
2. Description of the Related Art
In recent years, a semiconductor device having various functions, in which a plurality of circuits is integrated over an insulating surface, has been developed. In addition, a semiconductor device capable of transmitting and receiving of data, which is provided with an antenna and operates with electrical energy into which electric wave received by the antenna has been converted, has been developed. Such a semiconductor device is referred to as a wireless chip (also referred to as an ID tag, an IC tag, an IC chip, an RF (radio frequency) tag, a wireless tag, an electronic tag, or an RFID (radio frequency identification)), and has already been introduced into some markets.
Most of these semiconductor devices that have already been put into practical use have an antenna and a circuit (also referred to as an IC (integrated circuit) chip) using a semiconductor substrate such as a silicon substrate. The IC chip includes a memory circuit (also referred to as a memory), a control circuit, and the like. In particular, it is possible to provide a semiconductor device with higher performance and high added value by being provided with a memory circuit which can store much data. However, despite that silicon substrates are expensive, these semiconductor devices are required to be manufactured at low cost. This is because small semiconductor devices such as a wireless chip are expected to be in demand as semi-disposable products. As a result, in recent years, an organic thin film transistor (hereinafter, also referred to as an “organic TFT”), an organic memory, and the like using organic compounds for a control circuit, a memory circuit, and the like have been actively developed (for example, see Patent Document 1: Japanese Published Patent Application No. 2002-26277).
A memory element that functions as a memory portion of an organic memory is formed by providing an organic compound layer between a pair of electrodes, and data are written to the memory element utilizing change in an electrical characteristic such as a resistance value which is caused by application of voltages. Such an organic compound layer is generally formed by an evaporation method.
When an organic compound layer is formed by an evaporation method, only part of the vaporized organic compound is used, which leads to low efficiency in the use of materials. There is also a problem in that for example since materials which are not used are also vaporized, a large amount of energy is consumed in a manufacturing process.
In addition, when an organic memory is manufactured by an evaporation method using a metal mask, an alignment step for aligning the metal mask is required. Therefore, manufacturing yield is reduced due to bad alignment.